Answer to Question #14132 Submitted to "Ask the Experts"

I need to sample air for nickel-63 (⁶³Ni). Is there a recommended medium (i.e., cartridge) that should be used to draw air through?

The answer to your question depends somewhat on the method you intend to use to quantify the ⁶³Ni after it has been collected. I assume that the ⁶³Ni is associated with airborne particulates. Cartridges offer no significant advantages for particulate collection and are not typically used for collection of ⁶³Ni particulates from air because of the difficulty in counting the ⁶³Ni in a cartridge geometry. High efficiency air filters are preferable and are the most common choices for air sampling of particulate ⁶³Ni aerosols.

As you are likely aware, ⁶³Ni is a pure beta emitter with very low energy, 66 kiloelectronvolt (keV) maximum beta energy and about 17 keV average energy, and this limits appropriate analytical techniques. The most common analytical method is liquid scintillation counting (LSC). In such a case you may have the option of different filter types, depending on your needs and preferences. High efficiency glass fiber filters are among the most commonly used because they have high collection efficiency, can tolerate acceptably high filter loading (important in dusty environments), and exhibit a reasonable pressure drop so that fairly high air flow rates may be used. Such filters are insoluble and marginally light-transmissive in typical LSC solvents. Some membrane filters, such as cellulose nitrate are often transparent, and if the proper LSC cocktail is used, sometimes soluble in the cocktail. This makes for typically higher counting efficiency (more like 4 pi geometry compared to 2 pi for a glass fiber filter). Membrane filters are often more airflow-restrictive, especially in dusty environments, and some types are less rugged than glass fiber filters.

An alternative counting technique uses an internal proportional counter (IPC) in which the counter has no window, and the sample is loaded into the counting chamber and the sample holder is held in a temporary gas-sealed configuration while the proportional counter operates. Membrane filters are often preferred when using this technique because they usually exhibit somewhat better surface collection properties than do glass fiber filters, and this can yield somewhat higher counting efficiencies for low energy beta emitters. Typical IPCs provide 2 pi counting geometry. IPCs may require more maintenance to keep them in proper operating condition because of the significant probability of introducing contamination, possibly both radioactive and nonradioactive, into the counting chamber.

Other specialized collection and counting procedures are possible but uncommon and beyond the scope of this discussion. I hope this is helpful.

George Chabot, PhD, CHP